In a 'Juvia Gets Drunk' fanfiction, Juvia would most likely interact with the members of Fairy Tail. She might start bothering Natsu, asking him silly questions like if he can really breathe fire while drunk. She could also interact with Happy, and they might get into some sort of funny exchange, like Juvia trying to teach Happy a new song she made up in her drunken state. And of course, she'll interact with Cana. Cana being the drinker she is, might find Juvia's drunk behavior either hilarious or relatable and they could have a long chat about different kinds of drinks.
The relationship can start with mutual curiosity. Naruto is curious about Juvia's magic and Juvia about Naruto's ninja abilities. They begin to exchange knowledge, which brings them closer.
Their relationship would likely become more serious. They would have to think about not just themselves but also their baby. There would be more commitment and responsibility between them.
The novel Battle Through the Heavens could be exempted from reading. This novel was written by Tian Can Tudou. It described how after the young Xiao Yan suffered all kinds of blows, he suddenly obtained the help of a wisp of a ghost and opened a brand new door. The story took place in a world of battle aura. There were no fancy magic spells, only battle aura that multiplied to the peak. If you want to read the novel Battle Through the Heavens, you can skip reading the full text in the link provided.
In her final moments, Juvia could be holding Gray's hand tightly. She tells him not to blame himself and that she is doing this willingly. She might recall all the times she tried to get closer to him, and now she is making the ultimate sacrifice. Her eyes could start to lose their light as she takes her last breath, but her love for Gray remains strong even in death.
Gray would be devastated. He might go into a state of deep depression, isolating himself from the rest of the Fairy Tail guild. He would blame himself for not being able to protect her, especially if her death was related to her love for him. Gray would probably be filled with anger as well, and he would vow to take revenge on whoever was responsible for her death.
Gray could be a great addition. Since Gray has a history with both Juvia and Lyon, his presence can add a lot of drama. For instance, his reaction to Juvia and Lyon getting closer could range from jealousy to acceptance, which would create different story arcs.